PREPARATION OF BARBITURATE

Aim: To prepare and submit the pure product of barbiturate from diethylmalonate.

Apparatus: Round bottomed flask, Condenser, Water bath, Beaker, Funnel, Glass rod

Chemicals: Diethyl malonate, urea, absolute ethanol

Principle:  

             Barbituric acid or malonylurea or 6-hydroxyuracil is an organic compound based on a pyrimidine heterocyclic skeleton. It is an odourless powder soluble in water. Barbituric acid is the parent compound of barbiturate drugs, although barbituric acid itself is not pharmacologically active. The compound was discovered by the German chemist Adolf von Baeyer on December 4, 1864, the feast of Saint Barbara (who gave the compound its namesake), by combining urea and malonic acid in a condensation reaction. Malonic acid has since been replaced by diethyl malonate,as using the ester avoids the problem of having to deal with the acidity of the carboxylic acid and its unreactive carboxylate. Barbituric acid can form a large variety of barbiturate drugs that behave as central nervous system depressants. Barbituric acid is one of four ingredients used to make riboflavin(vitaminB₂).

Procedure:

               Place 1.2 g of clean sodium metal into a 250 mL round-bottomed flask, fitted with a reflux condenser. Add 25 mL of absolute ethanol in one portion. If the reaction is unduly vigorous, immerse the flask momentarily in ice. When all the sodium has reacted, add 8 g (7.6 mL) of diethyl malonate, followed by a solution of 3 g of dry urea in 25 ml of hot absolute ethanol (70 °C). Shake the mixture well, and reflux it for 1 hour in an oil bath heated to 110 °C. White solid separates. Add 45 mL of hot (50 °C) water to the reaction mixture followed with concentrated hydrochloric acid (ca. 5 mL), with stirring, until the solution is acidic. Filter the resulting mixture and leave clear solution in the refrigerator overnight. Filter the solid on the Büchner funnel, wash it with cold water, drain well and then dry at 100 °C for 2 hours. Weigh the product, calculate the yield of barbituric acid and measure the m.p. (lit. melts with decomposition at 245 °C). The cyclization reaction and purity of final product could be monitored with thin layer chromatography – ethanol/CH₂Cl₂ (8:1).

                                                              

Calculation:

Molecular weight of Diethylmalonate = 160.17g/mol

Molecular weight of barbiturate  = 128.08gm/mol

160.17g/mol  of Diethylmalonate gives                      128.08gm/mol of barbiturate

8 g of Diethylmalonate                 X g  of barbiturate

X=8*128.08/160.17=6.39gm

Theoretical yield =6.39g

Practical yield=----------------- g

Percentage yield = practical yield/ theoretical yieldx100=------------------------------%w/w

Report: